Surface mount package

ABSTRACT

A surface mount package is provided that includes a first metal layer and a second metal layer configured to be electrically connected to the first metal layer. The surface mount package further includes a ceramic layer between the first and second metal layers. The ceramic layer has an opening therethrough.

BACKGROUND OF THE INVENTION

This invention relates generally to surface mount packages, and moreparticularly, to surface mount packages for two terminal devices such asdiodes.

Surface mount components or devices, and in particular, the use ofsurface mount packages allow smaller footprint designs with improvedfunctionality and increased mounting densities. For example, IntegratedCircuit (IC) mounting methods using surface mounting allow mounting ofpackages on both sides of, for example, a printed wiring board, therebyresulting in higher density mounting and reduced wire board size ascompared to through-hole mounting. These surface mount packages also arebecoming increasingly smaller and thinner to further provide this higherdensity mounting.

Surface mount packages include different isolated paths for electricalcurrent flow, for example, to an anode and cathode within the packages.Plastic is often used to form the surface mount package and may be usedto isolate the current flow. These surface mount packages are commonlyreferred to as plastic packages. Separate metal connection pads may beused to provide electrical connection to the anode and cathode. Further,vias, other conduits or sidewall metallization may be included toprovide electrical and/or thermal continuity between top metalconnection pads and backside metal connection pads of the surface mountpackage.

These surface mount packages may be used to mount thereon differenttypes of two terminal devices, such as, for example, diodes, and moreparticularly, light emitting diodes (LEDs). However, operation of someof these two terminal devices generates high levels of heat. Plasticpackages may not provide acceptable levels of thermal dissipation forsome of these devices and for certain applications. For example, certainhigh power devices may require thermal dissipation at levels higher thancan be provided using these plastic packages. Further, because plastichas a relatively high thermal resistance, the efficiency of devicesmounted within these packages may be reduced.

Additionally, it is difficult, if not impossible, to seal the plasticpackages for certain applications, for example, to hermetically seal theplastic packages. This is because at the higher temperatures needed tohermitically seal the package (e.g., 300-400 degrees Celsius soldertemperature), the plastic packages can melt.

Thus, these plastic packages may not be suitable for certainapplications and further may not provide acceptable operatingcharacteristics.

BRIEF DESCRIPTION OF THE INVENTION

According to an exemplary embodiment, a surface mount package isprovided that includes a first metal layer and a second metal layerconfigured to be electrically connected to the first metal layer. Thesurface mount package further includes a ceramic layer between the firstand second metal layers. The ceramic layer has an opening therethrough.

According to another exemplary embodiment, a surface mount package isprovided that includes a first lead frame and a second lead frameconfigured to be electrically connected to the first lead frame. Thesurface mount package further includes a ceramic layer between the firstand second lead frames. The ceramic layer is configured to electricallyisolate a positive side and a negative side of the lead frames.

According to yet another exemplary embodiment, a method formanufacturing a surface mount package is provided. The method includesproviding a first metal layer and providing a second metal layerelectrically connected to the first metal layer. The method furtherincludes providing a ceramic layer between the first and second metallayers. The ceramic layer has an opening therethrough and is configuredto electrically isolate a positive side from a negative side of thesurface mount package.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are elevation views of various embodiments illustratingsurface mounting of surface mount devices.

FIG. 2 is a cross-sectional elevation view of a surface mount packageconstructed in accordance with an exemplary embodiment of the invention.

FIG. 3 is a top plan view of the surface mount package of FIG. 2.

FIG. 4 is a cross-sectional elevation view of a surface mount packageconstructed in accordance with another exemplary embodiment of theinvention.

FIG. 5 is a top plan view of the surface mount package of FIG. 4.

FIG. 6 is a flowchart illustrating a process for manufacturing a surfacemount package in accordance with an exemplary embodiment of theinvention.

FIGS. 7A-7C are top plan views of arrays of surface mount packagesconstructed in accordance with exemplary embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A is a side elevation view of a surface mount arrangement whereina surface mount device 32 (e.g., a diode) within a surface mount package33 is mounted, for example, to a printed wiring board 38. Moreparticularly, the surface mount device 32 is mounted to mountingportions, for example, solder paste portions 34 on a top surface 36 ofthe printed wiring board 38. Further, and as shown in FIG. 1B, surfacemount devices 32 may be mounted to both the top surface 36 and a bottomsurface 40 of the printed wiring board 38.

Various embodiments of the present invention provide a surface mountpackage. In an exemplary embodiment, as shown in FIGS. 2 and 3, asurface mount package 30 generally includes a plurality of layersforming the surface mount package 30 and for mounting a surface mountdevice 32 thereto. Specifically, the surface mount package includes afirst layer 44 (e.g., a first metal layer), which in this embodiment isa metal lead frame, a second layer 46, which in this embodiment is aceramic layer, and a third layer 48, which in this embodiment is anothermetal lead frame. More particularly, the first layer 44, includes a gap,groove or channel 50 formed (e.g., etched) thereon to electricallyisolate an input side or positive side 52 and an output side or negativeside 54 of the surface mount package 30. Specifically, and as shown inFIG. 3, the input side 52 includes a plurality of anodes 56 formed aspart of the first layer 44 and the output side 54 includes a pluralityof cathodes 58 formed as part of the first layer 44.

In an exemplary embodiment, the first layer 44 is formed of a metal suchas copper, Kovar, or other metal alloy (e.g., nickel), or a combinationthereof. In general, the first layer 44 is formed as an etched leadframe constructed of any suitable electrically conducting material. Inthe exemplary embodiment, the second layer 46 is formed of a ceramicmaterial, for example, alumina, calcia, beryllium oxide, aluminumnitride, silicon nitride, or other suitable ceramic material. The secondlayer 46 is provided on top of the first layer 44, using any known andsuitable process, for example, using a brazing process. The second layer46 includes an opening 60 extending therethrough (e.g., a cutoutportion). In this exemplary embodiment, the opening 60 is configured ina circular shape and provides access therethrough to the first layer 44.Additionally a plurality of vias 62 (e.g., two vias) are providedthrough the second layer 46, which in one embodiment, are metal filledvias 62 configured to provide electrical connection and connectivitybetween the first layer 44 and the third layer 48. For example, the vias62 provide for connecting the surface mount device 32 to the anodes 56of the first layer 44. Additional or fewer vias 62 may be provided.Additionally, a metal portion 64 extending generally perpendicularlyfrom the first layer 44 may be provided (e.g., formed thereon) formounting the surface mount device 32 thereto and for raising the surfacemount device 32 above the second layer 46. However, as should beappreciated, the metal portion 64 may be removed with the surface mountdevice 32 mounted directly to the first layer 44.

A top and bottom surface of the second layer 46 may be metallized, usingany known process, for example, refractory metallization, to provideelectrical and thermal conductivity with the third and first layers 48and 44, respectively. Various metals may be used for metallization,including, for example, silver.

In this exemplary embodiment, the third layer 48 (e.g., a second metallayer) is also formed of a metal such as copper, Kovar, or other metalalloy (e.g., nickel), or a combination thereof. In general, the thirdlayer 48 is formed as an etched lead frame constructed of any suitableelectrically conducting material and provided on top of the second layer46 using any known and suitable process, for example, using a brazingprocess. The third layer 48 also includes an opening 66 that may beconfigured to receive therein or therethrough the surface mount device32. For example, the third layer 48 may be configured to form a framestructure surrounding a surface mount device 32 mounted in a cavitytherein. As shown in FIG. 3, the surface mount device 32 is mountedapproximately in the center of the cavity.

The frame structure may be configured having angled inner walls 68 thatinclude a reflective surface for redirecting and focusing light emittedfrom a surface mount device 32 therein, and more particularly, a lightemitting diode (LED). More particularly, the angled walls 68 may beformed from a reflective silicon (e.g., etched in a silicon wafer). Inan exemplary embodiment, the angled walls 68 are etched at an angle ofapproximately 60 degrees. An example of a light emitting diode packagehaving angled walls is described in co-pending and commonly owned U.S.patent application entitled “Light Emitting Diode Package” having Ser.No. 10/914,361. It should be noted that the first and second layers 44and 46 may define a submount portion with a frame portion defined by thethird layer 48 provided on top thereof.

The surface mount device 32 is connected to the input and output sides52 and 54 (e.g., positive and negative sides) using, for example, wirebonds 70 as is known. Specifically, a wire bond 70 may be connected froma terminal (e.g., positive terminal) of the surface mount device 32 to ametal pad (not shown) formed on the second layer 46 for connection tothe anodes 56 through the vias 62. For example, the metal pads may beprovided as part of the vias 62. Another wire bond 70 may be connectedfrom another terminal (e.g., negative terminal) of the surface mountdevice 32 through the opening 60 of the second layer 46 to the negativeside 54 of the first layer 44.

It should be noted that the openings 60 and 66 may be configured indifferent shapes. For example, as shown in FIGS. 4 and 5, a surfacemount package 80 may be provided such that the opening 60 is configuredin a circular shape and the opening 66 is configured in an oval shape. Ametal pad 82 may be provided and formed as part of the vias 62 asdescribed in more detail herein. Thus, the surface mount device 32 maybe mounted off center within the opening 66.

An exemplary process 90 for manufacturing a surface mount package 30 isshown in FIG. 6. Specifically, at 92, a first layer is formed, forexample, a metal lead frame is formed (e.g., cut) from a piece of metal.A pattern is then etched or cut into the first layer at 94. This mayinclude, for example, providing connection members, such as, anodes andcathodes to the lead frame and providing a gap, groove or channelbetween the anodes and cathodes to electrically isolate an input andoutput that may be provided by the anode and cathode, respectively.Additionally, a metal portion may be formed on top of the first layerfor later mounting thereon of a surface mount device as described inmore detail herein. Thereafter, at 96, a second layer is formed, forexample, a ceramic layer is formed. The second layer is metallized at98, and more particularly, a top and bottom surface of the second layeris metallized.

At 100, an opening is provide (e.g., cut) in the second layer andconfigured to receive therein a surface mount device or the metalportion of the first layer. Thereafter, vias or conduits are provided(e.g., cut) in the second layer at 102. These vias may be metal filledto provide electrical and thermal connection through the second layer.Additionally, metal pads may be formed as part of and on top of themetal filled vias. At 104, a third layer is formed, for example, anothermetal lead frame is formed (e.g., cut) from a piece of metal. A patternis then etched or cut into the third layer, and more particularly, at106 an opening is provided (e.g., cut) therein for receiving a surfacemount device. The opening may be formed having reflective angled wallsas described herein.

At 108, the three layers are connected, for example, by brazing withsilver at 400 degrees Celsius or higher. Alternatively, the layers maybe bonded together, for example, using a polymer or adhesive (e.g.,BCB). The three layers thereby form a surface mount package that may beused to mount a surface mount device therein, for example, a surfacemount diode, such as an LED or Zener diode. The surface mount device maybe connected to the surface mount package using wire bonds as is known.The surface mount package may then be connected or mounted, for example,to a printed wiring board.

It should be noted that the process 90 may be modified, for example, thesteps described may be performed in a different order as desired orneeded. For example, the first two layers may be connected beforeforming the third layer. Additionally, the methods of forming andcutting the layers may be provided using any known process as desired orneeded.

It should be noted that a plurality of surface mount packages 30 may beformed as an array 110 as shown in FIGS. 7A-7C having differentconfigurations. The surface mount packages 30 may be aligned in seriesor parallel as shown and as desired or needed.

Thus, a surface mount package for a surface mount device (e.g., surfacemount LED) is provided. The surface mount package generally includes aceramic layer between two metal layers, without the use of plastic. Thesurface mount package allows use in a wider range of applications.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A surface mount package comprising: a first metal layer; a secondmetal layer configured to be electrically connected to the first metallayer; and a ceramic layer between the first and second metal layers,the ceramic layer having an opening therethrough.
 2. A surface mountpackage in accordance with claim 1 wherein the first and second metallayers comprise lead frames.
 3. A surface mount package in accordancewith claim 1 wherein the second metal layer comprises an opening havinggenerally the same size as the opening of the ceramic layer.
 4. Asurface mount package in accordance with claim 1 wherein the secondmetal layer comprises an opening having a larger size than the openingof the ceramic layer.
 5. A surface mount package in accordance withclaim 1 wherein the first metal layer comprises a gap configured toisolate an input side and an output side of the first layer.
 6. Asurface mount package in accordance with claim 1 wherein the ceramiclayer comprises a plurality of vias.
 7. A surface mount package inaccordance with claim 1 wherein the second metal layer comprises anopening having a generally circular shape.
 8. A surface mount package inaccordance with claim 1 wherein a top and bottom surface of the ceramiclayer are metallized.
 9. A surface mount package in accordance withclaim 1 wherein the first metal layer comprises a plurality of anodesand a plurality of cathodes that are electrically isolated.
 10. Asurface mount package in accordance with claim 1 further comprising ametal portion extending from the first metal layer into the opening ofthe ceramic layer and configured to mount a surface mount devicethereto.
 11. A surface mount package in accordance with claim 1 whereinthe second metal layer comprises an opening having angled inner walls.12. A surface mount package in accordance with claim 1 wherein the firstmetal layer is configured to mount a surface mount device thereto.
 13. Asurface mount package in accordance with claim 1 further comprising atleast one metal pad on a top surface of the ceramic layer and wherein asurface mount device is connected via a wire bond to the at least onemetal pad.
 14. A surface mount package in accordance with claim 1wherein the ceramic layer is configured to electrically isolate a firstset of terminals and a second set of terminals of the first metal layer.15. A surface mount package comprising: a first lead frame; a secondlead frame configured to be electrically connected to the first leadframe; and a ceramic layer between the first and second lead frames, theceramic layer configured to electrically isolate a positive side and anegative side of the lead frames.
 16. A surface mount package inaccordance with claim 15 further comprising an opening in the secondlead frame and a corresponding opening in the ceramic layer.
 17. Asurface mount package in accordance with claim 15 wherein the first leadframe comprises a gap configured to electrically isolate the positiveside and the negative side of the lead frames.
 18. A method formanufacturing a surface mount package, the method comprising: providinga first metal layer; providing a second metal layer electricallyconnected to the first metal layer; and providing a ceramic layerbetween the first and second metal layers, the ceramic layer having anopening therethrough and configured to electrically isolate a positiveside from a negative side of the surface mount package.
 19. A method inaccordance with claim 18 further comprising forming a gap within thefirst metal layer to electrically isolate the positive side from thenegative side.
 20. A method in accordance with claim 18 furthercomprising providing an opening in both the second metal layer andceramic layer configured to receive a surface mount device for mountingto the surface mount package.